Recently, mobile information terminals represented by portable telephones have come into widespread use. As shown in FIGS. 1A, 1B, such portable telephones are provided with display devices 11, 21 for displaying information and an input device composed of operation keys 12, 22, a pointing device (not shown) and the like. Portable telephone 10, which is entirely encased in a single housing as shown in FIG. 1A, is known as one of portable telephones. Folding portable telephone 20, which has two casings that are jointed by a hinge as shown in FIG. 1B and which can be changed between an open state in which both casings are side by side, and a folded state in which both casings are folded together for convenience of portability, is also known. In either case, display devices 11, 21 and the input device are usually disposed on the same side as each other so that a user can operate the input device while viewing display devices 11, 21. Further, keys and a pointing device may be arranged on a side surface facing a direction that is perpendicular to the surface on which display device 11, 21 are disposed.
In contrast, a mobile information terminal, in which some operation keys are arranged on the rear surface (a surface placed back to back with the display surface of a display device) of a surface on which a display surface of a display device is disposed, is disclosed in Japanese Patent Application Laid-Open No. 2000-236376. Further, a mobile information terminal, in which a touch panel is arranged on a rear surface, is disclosed in Japanese Patent Application Laid-Open No. 2002-77357.
However, configurations, in which an input device is arranged either on the same surface as the display surface of a display device of a mobile information terminal or on a side surface, as in the general prior art, have the following drawbacks:
(1) When a user holds a mobile information terminal in his/her hand, fingers of the hand holding the mobile information terminal extend around the rear side of the mobile information terminal. Therefore, superior ease of operation cannot be achieved when the user wants to operate an input device disposed on the side of a display surface of a display device with one hand holding the mobile information terminal.(2) In a case where an input device is disposed on the side surface of a mobile information terminal, because the side surface is narrow and provides a restricted area for disposing the device, when an input device for performing a complicated input operation, for example, a pointing device to input values of two-dimensional coordinates is disposed on the side surface, an operation to input information into the device by hand is apt to be difficult. In particular, an operation that uses the finger(s) of one hand holding the mobile information terminal is apt to be difficult.(3) In a case in which the user operates a mobile information terminal with the fingers of one hand holding the mobile information terminal in a condition in which the user holds a mobile information terminal in his/her hand, the user is only able to operate the terminal with some of his/her fingers, for example, an index finger, the thumb or the like, because the fingers of the hand are used to hold the mobile information terminal. Therefore, operation efficiency is apt to be reduced.(4) In a case in which a user performs an input operation while holding a mobile information terminal in his/her hand, when the user performs an input operation with a hand that is different from the hand holding the mobile information terminal in order to avoid the problems (1) to (3), the user has both hands fully occupied. Therefore, the user cannot use the hand(s) for other tasks. Further, there are cases where a user may wish to operate a mobile information terminal in a condition in which only one hand can be used, for example, a case where the user operates a mobile information terminal while holding a bag. In this case, the user is forced to perform an input operation with one hand that holds a mobile information terminal.(5) In cases where a display device and an input device are disposed on the same surface as each other, there is mutual competition for installation of each device on the area of the terminal whose size is limited so that the mobile information terminal can be manufactured in a compact configuration as a portable device. Under these circumstances, when the display device is made large to improve visibility, the installation space for the input device is narrowed, thus sacrificing ease of operation. On the other hand, when the input device is made large to improve operability, visibility is sacrificed.(6) In a case where a display device and an input device are disposed on the same surface as each other, when both are made large to improve both operability and visibility, the mobile information terminal itself is required to be made large. Therefore, portability is reduced.
In contrast, in the prior art disclosed in above-mentioned Japanese Patent Application Laid-Open No. 2000-236376 and Japanese Patent Application Laid-Open No. 2002-77357, the installation area for input devices disposed on a front side can have a margin to some degree by arranging a part of the input devices on a rear side, and thus operability can be improved to some extent.
However, in Japanese Patent Application Laid-Open No. 2000-236376, only limited kinds of input devices are arranged on a rear side such as a scroll key, a determination key, a clear key and the like, and most of the keys are still arranged on the front side. On the other hand, when operating keys arranged on the rear side, since an operator views the display device that is arranged on the front side, the operator cannot view his/her finger as it operates keys arranged on the rear side. Therefore, in cases where an increased numbers of keys are arranged on the rear side, the input operation becomes difficult.
Further, in Japanese Patent Application Laid-Open No. 2002-77357, as shown in FIGS. 2A and 2B, in mobile information terminal 30, touch panel 32 is disposed on surface 30b opposite to surface 30a on which display device 31 is disposed. This touch panel 32 is used to select one item among selection items that are displayed on display device 31 by touching the location on the rear side that is reverse to the location where the item to be selected is displayed. In this configuration, various input operations can be performed by using touch panel 32 disposed on the rear side. However, because the operator cannot view the finger with which he/she is performing the operation, the operator cannot determine precisely where the finger has been placed until the operation to select one item has been completed. Therefore, particularly in cases where there are many items to be selected and which are located in a narrow area, a mistake may be made in touching the location of the item to be selected, and as a result, an item different from the one intended is selected. Therefore, there is a problem in operability.
Further, there are cases where an operator can perform an input operation without viewing a display device during the input operation of a mobile information terminal, for example, in cases where the operator inputs a specific keyword. In this case, when the input device is disposed on the rear side, it may be more convenient for the operator to perform an input operation while viewing the rear side. However, mobile information terminal 30 disclosed in Japanese Patent Application Laid-Open No. 2002-77357 is not suitable for operating touch panel 32 disposed on surface 30b of the rear side while viewing mobile information terminal 30 from surface 30b of the rear side. That is, in mobile information terminal 30 disclosed in Japanese Patent Application Laid-Open No. 2002-77357, for example, when an input operation that uses alphabet is performed by using touch panel 32 of the rear side, as shown in FIG. 2A, the layout of areas that are used to input each letter, while mobile information terminal 30 is viewed from surface 30b of the rear side, is a mirror image of the layout of areas that are displayed on display device 30 while viewed from surface 30a of the front side. Therefore, a problem arises in that the input operation confuses the operator.